Aircraft navigation assistance device and method

ABSTRACT

The invention relates to an aircraft navigation aid method. It comprises the following steps of defining an area to be sensed to the right and to the left of a first hypothetical path of the aircraft, sensing, for each of the two areas to be sensed to the right and to the left, a corresponding predefined underlying relief, in order to identify dangerous sub-zones to the right and/or to the left, computing, for each of the dangerous sub-zones to the right and/or to the left, a time ΔT remaining to begin an avoidance maneuver before a point of no return, and determining for the dangerous sub-zones to the right a minimum ΔT denoted ΔT right and/or for the dangerous sub-zones to the left a minimum ΔT denoted ΔT left, establishing a navigation aid from ΔT right and/or ΔT left.

The invention relates to an aircraft navigation aid method.

The field of the invention is that of air navigation and safety aid and relates more particularly to ground avoidance maneuvers.

Onboard devices for performing vertical avoidance maneuvers are already known.

Such a device described in patent EP 0 565 399 comprises in particular a mass memory for storing topographical data representing a substantial portion of the surface of the earth, a fast-access working memory into which is transferred the topographical data corresponding to the flight area of the aircraft and means of predicting the path of the aircraft, based on status indications relating to the longitude, latitude, altitude, speed and acceleration of the aircraft. The planned path is compared to the topographical data in the fast-access memory; in the event of a potential collision with the ground, an alarm is triggered and a vertical avoidance maneuver is suggested to the pilot.

In some cases, particularly on approaches or take-offs in mountainous areas, the aircraft nears the ground without that fact constituting a threat or an abnormality. The collision-avoidance device is then set to a specific mode designed to reduce the rate of false alarms; however, when a threat is detected, the vertical avoidance maneuver is often no longer possible.

Another device described in patent EP 0 802 469, refining the above device, further suggests to the pilot a lateral avoidance maneuver when the vertical avoidance maneuver is no longer possible. A first and then a second alarm are triggered when the aircraft crosses respective thresholds of 20 then 5 seconds before the point of no return, in other words before the ultimate point from which an avoidance maneuver must absolutely have been started.

These predefined thresholds are not always suited to the area in which the aircraft is flying, and this device does not provide for continuous monitoring of how the danger changes; it does not truly quantify the danger, in other words continually determine the time remaining to undertake a lateral avoidance maneuver to the right or to the left before the point of no return.

An important object of the invention is therefore to determine continually the time remaining to undertake an avoidance maneuver before the point of no return.

To achieve these aims, the invention proposes an aircraft navigation aid method, mainly characterized in that it comprises the following steps consisting in:

-   a) defining an area to be sensed to the right and to the left of a     first hypothetical path of the aircraft, designated the feeler line     support path, -   b) sensing, for each of the two areas to be sensed to the right and     to the left, a corresponding predefined underlying relief, in order     to identify dangerous sub-zones to the right and/or to the left, -   c) computing, for each of the dangerous sub-zones to the right     and/or to the left, a time ΔT remaining to begin an avoidance     maneuver before a point of no return, and determining for the     dangerous sub-zones to the right a minimum ΔT denoted ΔT right     and/or for the dangerous sub-zones to the left a minimum ΔT denoted     ΔT left, -   d) establishing a navigation aid from ΔT right and/or ΔT left.

The method according to the invention thus comprises a number of steps mainly consisting in sensing along a feeler line support path of the aircraft and to each side of the latter, the relief underlying an area marked out by grids, for example, identifying the grids presenting a potential danger and, for these grids, the time remaining before undertaking an avoidance maneuver.

According to a feature of the invention, the feeler line support path is determined during a time T broken down into a pilot reaction time T_(reac), a time T_(pull) for placing the aircraft on a horizontal path and the time T_(roll) for placing the aircraft in a roll.

According to another feature of the invention, the dangerous sub-zones of step b) are identified according to a second hypothetical path of the aircraft such that:

-   if the aircraft is ascending, the ascent is stopped immediately, -   in other cases, the path is continued unchanged.

The purpose of this second hypothetical path is to increase the safety margin of the method.

The time ΔT of step c) is advantageously computed according to a hypothetical flight time toward a dangerous sub-zone, calculated according to a time T_(pull) to place the aircraft on a horizontal path and a time T_(roll) to place the aircraft in a roll:

-   in a horizontal plane when the aircraft is ascending or is flying     level, -   in a horizontal plane and in a vertical plane when the aircraft is     descending.

According to another feature of the invention, step d) comprises a step for comparing ΔT right and/or ΔT left with one or more predefined times and, where appropriate, a step consisting in determining the time remaining for the safest side (best lateral) from the maximum between ΔT right and/or ΔT left and the time remaining for the least safe side (worst lateral) from the minimum between ΔT right and/or ΔT left.

Another object of the invention is to produce an aircraft navigation aid device, comprising a mass memory designed to store a terrain database, a program memory comprising an application program of the method as described, a central processing unit designed to run the program and an input/output interface.

Other features and advantages of the invention will become apparent on reading the detailed description that follows, given by way of non-limiting example and with reference to the appended drawings in which:

FIG. 1 diagrammatically represents right and left rings Cr and Cl respectively in an unbalanced case,

FIGS. 2 a, 2 b diagrammatically represent, in a horizontal plane, examples of areas to be sensed in the case of an initial straight line (2 a) and turning (2 b) path and FIG. 2 c diagrammatically represents, in a vertical plane, an example of path supporting these areas to be sensed,

FIG. 3 diagrammatically represents the grid of the relief underlying a ring Cr,

FIGS. 4 a and 4 b respectively and diagrammatically represent, in a vertical then horizontal plane, path sections during defined times, and FIG. 4 c diagrammatically illustrates, in a horizontal plane, the time remaining for the best lateral and the worst lateral,

FIG. 5 diagrammatically represents an example of presentation of navigation aid information,

FIG. 6 diagrammatically represents an example of a device for implementing the navigation aid method as described.

The invention relates to an aircraft navigation aid; in the description that follows, an airplane will be taken as a typical aircraft. It will also be assumed that the navigation aid relates to the pilot; it may more generally relate to a piloting system in particular in the case of an automatic pilot.

The method according to the invention comprises a number of steps mainly consisting in sensing, along a hypothetical path of the aircraft and to each side of the latter, the relief underlying a strip of terrain identified by grids, identifying the grids presenting a potential danger and, for these grids, the time remaining before undertaking an avoidance maneuver.

The first step consists in defining an area to be sensed to the right and to the left of a hypothetical path of the airplane which is designated in the description below as a feeler line support path and which is determined for a time T as will be seen later.

The term feeler line or area to be sensed is the shape defined by a succession of rings along this feeler line support path.

Two rings, respectively right Cr and left Cl, are represented in FIG. 1. The diameter D of each ring is of the form: D=d+HSM+HPU d being the diameter of the avoidance maneuver circle, HSM being a horizontal safety margin, HPU being a horizontal position uncertainty.

For an Airbus 340, for example, HSM=220 m and HPU=100 m.

As can be seen in FIG. 1, the right and left rings Cr and Cl respectively overlap the feeler line support path; they also overlap each other when they are not offset as shown in this FIG. 1. Only the right and left avoidance circles are tangential to the path and tangential to each other when the rings are not offset.

From the current position of the aircraft, the right rings succeed each other continuously, remaining tangential to the feeler line support path; the same applies for the left rings Cl. FIG. 2 a shows three left rings Cl succeeding each other at times t, t′ and t″. These successions of rings occurring between the time t0 corresponding to the current position of the airplane and a time T defined later thus define an area to be sensed to the right and to the left represented in a horizontal plane in FIGS. 2 a and 2 b according to whether the initial path of the airplane is straight or turning. These areas to be sensed are in the form of strips.

The feeler line support path of the airplane is determined during a time T=T_(reac)+T_(pull)+T_(roll), the path sections respectively corresponding to these times T_(reac), T_(pull) and T_(roll) as represented in a vertical plane in FIG. 2 c. The terms are defined as follows:

-   -   T_(reac) is the reaction time of the pilot (or of the piloting         unit) before starting the avoidance maneuver, in other words the         time during which the airplane continues on its path without         changing parameters (speed unchanged as an absolute value, turn         radius unchanged if the airplane is turning, gradient unchanged         if the airplane is descending). This time T_(reac) is defined by         default; as an example T_(reac)=25 sec could apply when the         aircraft is descending and T_(reac)=0 sec could apply when the         airplane is ascending,     -   T_(pull) is the time needed for the airplane to perform a         pull-out in the vertical plane, in other words to return to a         horizontal path when the airplane is initially descending or         ascending; when the situation demands a lateral avoidance         maneuver, the pilot will first of all make himself safe with         respect to the relief in the vertical plane by stopping the         vertical change as early as possible; conventionally,         T_(pull)=|γ₀|×V/fcv, γ₀ being the gradient of the airplane, V         its current speed and fcv its vertical loading factor.     -   T_(roll) is the time to place the airplane in a roll in order to         perform an avoidance turn (or circle); placing in a roll         consists in changing the roll from its initial value to a final         value equal, for example, to ±33° (the sign depending on the         direction of turn toward the right or toward the left) taking         into account a roll rate equal, for example, to 7°/sec for an         A340 type airplane. T_(roll) can be equal to 0 when the placing         in a roll coincides with the current turn of the airplane.         Although placing in a roll is translated by a placing in a turn,         it is artificially assumed that the feeler line support path         during this time T_(roll) is the same as the current path and is         therefore straight if the current path of the airplane was         straight; this represents an additional safety margin.

As is represented in the horizontal plane in FIG. 2 a, when the current path of the airplane is straight, in other words presenting a roll angle less than 1° for example, the time T_(reac)+T_(pull)+T_(roll) for each of the rings is the same to the right and to the left of the feeler line support path and the areas to be sensed to the right and to the left are the same.

When the current path of the airplane is a turn, as is represented in the horizontal plane in FIG. 2 b in the case of a current turn to the right, the areas to be sensed to the right and to the left differ not only for obvious reasons of geometry but also because the time T_(reac)+T_(pull)+T_(roll) differs between a ring to the right and a ring to the left. In practice, the times T_(reac) and T_(pull) are the same; however, when the placing in a roll consists in continuing or accentuating the roll of the current turn, the time to place in a roll is less than the contrary case for which it is first of all necessary to reestablish a straight line path before placing in the required roll opposite to the roll of the current turn. There is then a distinction between a time to place in a roll to the right T_(rollr) and a time to place in a roll to the left T_(roll). In the case of a current turn to the right as represented in FIG. 2 b, T_(rollr)<T_(rolll).

Furthermore, it is preferably planned that the speed V_(turn) at which the maneuver is performed during T_(rolll) or T_(rollr) is equal to the speed of the airplane in its current position uprated by x% (x%=10%, for example).

This speed variation occurs during T_(reac)+T_(pull). The feeler line support path then comprises two parts: the point C is the center of the circle representing the feeler line support path during T_(reac)+T_(pull) and C′ is the center of the circle representing the feeler line support path during T_(rollr) or T_(rolll), the turn being performed at the speed V_(turn). Although the path during T_(reac)+T_(pull) is not exactly a circle, since the speed varies, it is sufficiently close to a circle for this approximation to be made.

Overall, the feeler line support path is, in the horizontal plane, the continuation of the current straight line or turn (to within this approximation), during T_(reac)+T_(pull)+T_(roll). In the vertical plane, the vertical change is stopped to return to a horizontal path, during T_(reac)+T_(pull) when the airplane is descending and during T_(pull) when the airplane is ascending (which corresponds to the worst case ascending).

The airplane moreover has a terrain database comprising topographical data representative of the relief of the earth and in particular of that over which the airplane is or will be flying. This digitized topographical data is conventionally identified according to a grid reference.

In a second step, this topographical data is used to determine the potential dangers of the relief underlying the areas to be sensed to the right and to the left.

To do this, the areas to be sensed are parameterized so that the digitized relief grids corresponding to these areas, and all the grids in which at least one peak belongs to an area to be sensed are sensed, can be extracted from the terrain database. FIG. 3 represents, in the horizontal plane, the grids corresponding to a right ring Cr and the grids of preceding rings.

For each grid tested, the potential danger is determined by comparing Z_(critical) to Z_(relief)+VSM,

-   Z_(relief) being the altitude of the grid concerned, -   VSM being a vertical safety margin varying, for example, with the     distance between the airplane and the nearest airport, this safety     margin typically being 100 m, -   and Z_(critical) being a hypothetical altitude defined as being the     altitude that the airplane would have when flying over the grid in     the case where: -   if it is ascending, the ascent would be stopped immediately, -   if it is descending, the descent would be continued unchanged, -   if it is flying level, the level would be continued unchanged.

Thus, the lateral grids presenting a danger, in other words grids for which Z_(critical)<Z_(relief)+VSM, are identified. These dangerous grids can be highlighted, in particular displayed on a screen for the attention of the pilot.

For each of the dangerous grids, a third step is used to calculate the time ΔT remaining before the start of the avoidance maneuver, in other words the maximum reaction time T_(reac) that the pilot has before performing a pull-out in the vertical plane.

This remaining time ΔT is calculated by reconstructing a hypothetical flight time toward the point considered dangerous, in other words the obstacle of the dangerous grid. This flight time is calculated in the vertical plane as illustrated in FIG. 4 a; it is also calculated in the horizontal plane as illustrated in FIG. 4 b, distinguishing the case of a straight-line flight from that of a turning flight.

The time ΔT is equal to the maximum of the corresponding times in the horizontal plane and in the vertical plane for the case where the airplane is descending, and to the horizontal flight time only for the case where the airplane is ascending or flying level.

-   -   ΔT_(h str) ascending, straight     -   ΔT_(h turn) ascending, turning     -   ΔT=max(ΔT_(h str), ΔT_(v)) descending, straight     -   max (ΔT_(h turn), ΔT_(v)) descending, turning,         ΔT_(h str) defining the time remaining in the horizontal plane         when the current path of the airplane is straight,         ΔT_(h turn) defining the time remaining in the horizontal plane         when the current path of the airplane is turning, ΔT_(v)         defining the time remaining in the vertical plane regardless of         the current path of the airplane. It is more specifically the         time remaining for the pilot before performing a pull-out to         obtain a horizontal path in order, without any lateral avoidance         maneuver, to avoid the obstacle identified in the grid         considered dangerous, taking into account a vertical safety         margin VSM: in practice, normally max(ΔT_(h), ΔT_(v))=ΔT_(h)         applies, unless, as is represented in FIG. 4 a, ΔT_(v) enables         the pilot to fly over the obstacle.

We have: ${\Delta\quad T_{hstr}} = {\frac{D - R_{\varphi\quad f} - {HSM} - {HPU}}{V} - T_{pull} - T_{roll}}$ ${\Delta\quad T_{hturn}} = {\frac{2R_{\varphi\quad i}*{\arcsin\left( \frac{D - R_{\varphi\quad f} - {HSM} - {HPU}}{2R_{\varphi\quad i}} \right)}}{V} - T_{pull} - T_{roll}}$ with, as indicated in FIG. 4 b in the case of a straight line path, D being the distance between the current position of the airplane and the obstacle, R_(φf) being the radius of the avoidance circle, R_(φi) being the radius of the current turn, HSM being a horizontal safety margin and HPU being uncertainty concerning the current position and V being the current speed of the airplane; ΔT_(h turn)=T_(reac) is assumed if arcsin is undefined. ${{And}\quad\Delta\quad T_{v}} = \frac{z - \left( {z_{terrain} + {VSM}} \right) - {\frac{V^{2}}{fcv}\left( {1 - {\cos\quad\gamma_{0}}} \right)}}{{- V}\quad\sin\quad\gamma_{0}}$ with, as indicated in FIG. 4 a, z being the current altitude of the airplane, z_(terrain) being the altitude of the obstacle, VSM being a vertical safety margin, V being the current speed of the airplane, fcv being the vertical loading factor of the airplane and γ₀ being its gradient.

For each of the left and right sides, the minimum of these ΔT values is then identified over all of the dangerous grids, and it is designated ΔT_(right) and ΔT_(left).

These ΔT_(right) and ΔT_(left) values correspond to the nearest dangerous right and left grids, as illustrated in FIG. 4 c; here, too, these grids can be highlighted, for the attention of the pilot.

It may be that one of these ΔT_(right) or ΔT_(left) values does not exist when, for example, no dangerous grid has been identified on one side.

As illustrated in the horizontal plane in FIG. 4 c, the time remaining for the most critical side, in other words the least safe side (the right side in the figure), called the worst lateral (WL), is the one corresponding to the minimum between ΔT_(right) and ΔT_(left) and the time remaining for the safest side (left side in the figure), called the best lateral (BL), is that corresponding to the maximum reaction time T_(reac) which is equal to the maximum between ΔT_(right) and ΔT_(left).

The fourth step corresponding to an alert management step then begins.

When BL and WL exist, they are compared to predefined times, such as, for example, a time T_(caution) and a time T_(warning). As an example, T_(caution)=20 sec and T_(warning)=8 sec.

Four classes can then be distinguished for each side:

-   “Infinite” when BL (or WL) is greater than T_(caution), -   “Danger” when BL (or WL) is less than or equal to T_(caution) and     greater than T_(warning), -   “Critical” when BL (or WL) is less than or equal to T_(warning) and     greater than 0 seconds, -   “Fatal” or “impossible” when BL (or WL) is less than or equal to 0     seconds.

The same classes can also be defined for a vertical time remaining T_(v); the aforementioned patents should be referred to for information on how to compute T_(v).

By combining these four classes for each of the Tv, BL and WL, subclasses are obtained, to which are linked notices and/or advice and/or orders, as indicated in the table below, in which the sub-classes are identified by numbers ranging from 1 to 40. Best Worst lateral lateral Vertical (“BL”) (“WL”) Notice Advice Command 1 Infinite Infinite Infinite Continue on path 2 Infinite Infinite Danger Caution WL Continue on path (avoid turn WL) 3 Infinite Infinite Critical Warning WL Continue on path (avoid turn WL) 4 Infinite Infinite Impossible Avoid WL Continue on path (avoid turn WL) 5 Infinite Danger Danger Caution Lateral Continue on path (avoid turn lateral) 6 Infinite Danger Critical Warning WL/Caution BL Continue on path (avoid turn lateral) 7 Infinite Danger Impossible Avoid WL/Caution BL Continue on path (avoid turn lateral) 8 Infinite Critical Critical Warning Lateral Continue on path (avoid turn lateral) 9 Infinite Critical Impossible Avoid WL/Warning BL Continue on path (avoid turn lateral) 10 Infinite Impossible Impossible Avoid Lateral Continue on path (avoid turn lateral) 11 Danger Infinite Infinite Caution Vertical Climb (or turn BL) Dangerous terrain 12 Danger Infinite Danger Caution Vertical and WL Climb (or turn BL) Dangerous terrain 13 Danger Infinite Critical Warning WL/Caution Vertical Climb (or turn BL) Dangerous terrain 14 Danger Infinite Impossible Avoid WL/Caution Vertical Climb (or turn BL) Dangerous terrain 15 Danger Danger Danger Caution Vertical and Lateral Climb (or turn quickly BL) Dangerous terrain 16 Danger Danger Critical Warning WL/Caution Vertical and BL Climb (or turn quickly BL) Dangerous terrain 17 Danger Danger Impossible Avoid WL/Caution Vertical and BL Climb (or turn quickly BL) Dangerous terrain 18 Danger Critical Critical Warning Lateral/Caution Vertical Climb (or turn immediately BL) Dangerous terrain 19 Danger Critical Impossible Avoid WL/Warning BL/Caution Vertical Climb (or turn immediately BL) Dangerous terrain 20 Danger Impossible Impossible Avoid Lateral/Caution Vertical Climb (avoid turn lateral) Dangerous terrain 21 Critical Infinite Infinite Warning Vertical Climb immediately (or turn BL) Ascend 22 Critical Infinite Danger Warning Vertical/Caution WL Climb immediately (or turn BL) Ascend 23 Critical Infinite Critical Warning Vertical and WL Climb immediately (or turn BL) Ascend 24 Critical Infinite Impossible Avoid WL/Warning Vertical Climb immediately (or turn BL) Ascend 25 Critical Danger Danger Warning Vertical/Caution Lateral Climb immediately (or turn rapidly BL) Ascend 26 Critical Danger Critical Warning Vertical and WL/Caution BL Climb immediately (or turn rapidly BL) Ascend 27 Critical Danger Impossible Avoid WL/Warning Vertical Climb immediately (or turn rapidly BL) Ascend 28 Critical Critical Critical Warning Vertical and Lateral Climb immediately (or turn immediately BL) Ascend 29 Critical Critical Impossible Avoid WL/Warning Vertical and BL Climb immediately (or turn immediately BL) Ascend 30 Critical Impossible Impossible Avoid lateral/Warning Vertical Climb immediately (avoid turn lateral) Ascend 31 Impossible Infinite Infinite Avoid Vertical Turn BL Turn BL 32 Impossible Infinite Danger Avoid Vertical/Caution WL Turn BL Turn BL 33 Impossible Infinite Critical Avoid Vertical/Warning WL Turn BL Turn BL 34 Impossible Infinite Impossible Avoid Vertical and WL Turn BL Turn BL 35 Impossible Danger Danger Avoid Vertical/Caution Lateral Turn rapidly BL Turn BL now 36 Impossible Danger Critical Avoid Vertical/Warning WL/Caution BL Turn rapidly BL Turn BL now 37 Impossible Danger Impossible Avoid Vertical and WL/Caution BL Turn rapidly BL Turn BL now 38 Impossible Critical Critical Avoid Vertical/Caution Lateral Turn immediately BL Turn BL immediately 39 Impossible Critical Impossible Avoid Vertical and WL/Warning BL Turn immediately BL Turn BL immediately 40 Impossible Impossible Impossible Collision with terrain Collision with terrain Collision with terrain

Information obtained from this table can be displayed, for example, in the form of colored areas, the fill pattern of which is proportional to the respective values of Tv, ΔT_(right) and ΔT_(left). An example of how this information could be presented is illustrated in FIG. 5.

There now follows a description of the lateral avoidance maneuver proper, occurring at the end of a time less than or equal to T_(reac) maximum+T_(pull)+T_(roll).

It concerns a circular maneuver accomplished in the horizontal plane tangential to the preceding path section, in the direction corresponding to that recommended after the preceding step and for which the radius R conventionally takes the form: R=V _(turn) ²./(g.tang φ) V_(turn) being the turning speed, g being the gravitational acceleration (g=9.81 m/s²), φ being the roll angle.

The speed V_(turn) at which the turn is made is equal to the speed of the airplane in its current position, uprated by 10%, for example, while being limited to a maximum V_(max) dependent on regulations and on the configuration of the airplane. For example, for an A340 type airplane, V_(max) varies according to its configuration (landing gear down and/or flaps deployed) between 180 knots and 205 knots (1 knot≅1852 m/h).

The method according to the invention is implemented in a navigation aid device preferably on board the airplane; the device may, if necessary, be part of an aircraft radio control system.

As is represented in FIG. 6, the navigation aid device 1 conventionally comprises at least a mass memory 2 designed to store a terrain database, a program memory 3 comprising an application program of the method described, a central processing unit 4 designed to run the program and an input-output interface 5.

The computations are overall performed, for example, at 100-millisecond intervals. 

1. An aircraft navigation aid method, comprising the steps of: a) defining an area to be sensed to the right and to the left of a first hypothetical path of the aircraft, designated the feeler line support path, b) sensing, for each of the two areas to be sensed to the right and to the left, a corresponding predefined underlying relief, in order to identify dangerous sub-zones to the right and/or to the left, c) computing, for each of the dangerous sub-zones to the right and/or to the left, a time ΔT remaining to begin an avoidance maneuver before a point of no return, and determining for the dangerous sub-zones to the right a minimum ΔT denoted ΔT right and/or for the dangerous sub-zones to the left a minimum ΔT denoted ΔT left, d) establishing a navigation aid from ΔT right and/or ΔT left.
 2. The method as claimed in claim 1, wherein the feeler line support path is determined during a time T broken down into a pilot reaction time T_(reac), a time T_(pull) for placing the aircraft on a horizontal path and a time T_(roll) for placing the aircraft in a roll.
 3. The method as claimed in claim 1, wherein an area to be sensed to the right and/or to the left is defined according to rings succeeding one another, each ring presenting a diameter D in the form D=d+safety margin, d being the diameter of a circular avoidance maneuver.
 4. The method as claimed in claim 1, wherein the areas to be sensed are defined according to the current straight-line or turning path of the aircraft.
 5. The method as claimed in claim 1, wherein it comprising a step prior to step b) of parameterizing the areas so that the relief underlying these areas can be sensed.
 6. The method as claimed in claim 5, wherein the areas and the relief are parameterized according to a grid reference.
 7. The method as claimed in claim 1, wherein the dangerous sub-zones of step b) are identified according to a second hypothetical path of the aircraft such that: if the aircraft is ascending, the ascent is stopped immediately, in other cases, the path is continued unchanged.
 8. The method as claimed in claim 1, wherein the time ΔT of step c) is computed according to a hypothetical flight time toward a dangerous sub-zone, calculated according to a time T_(pull) to place the aircraft in a horizontal path and a time T_(roll) to place the aircraft in a roll: in a horizontal plane when the aircraft is ascending or flying level, in a horizontal plane and in a vertical plane when the aircraft is descending.
 9. The method as claimed in claim 1, wherein step d) comprises a step for comparing ΔT right and/or ΔT left with one or more predefined times.
 10. The method as claimed in claim 1, wherein step d) comprises a step of determining the time remaining for the safest side (best lateral) (safer) from the maximum between ΔT right and/or ΔT left and the time remaining for the least safe side (worst lateral) (less) from the minimum between ΔT right and/or ΔT left.
 11. The method as claimed in claim 1, wherein it comprises a step consisting in generating a lateral avoidance maneuver.
 12. An aircraft navigation aid device, comprising a mass memory designed to store a terrain database, a program memory comprising an application program of the method as claimed in claim 1, a central processing unit designed to run the program and an input-output interface.
 13. The method as claimed in claim 2, wherein an area to be sensed to the right and/or to the left is defined according to rings succeeding one another, each ring presenting a diameter D in the form D=d+safety margin, d being the diameter of a circular avoidance maneuver.
 14. The method as claimed in claim 2, wherein the areas to be sensed are defined according to the current straight-line or turning path of the aircraft.
 15. The method as claimed in claim 3, wherein the areas to be sensed are defined according to the current straight-line or turning path of the aircraft.
 16. The method as claimed in claim 3, wherein it comprising a step prior to step b) of parameterizing the areas so that the relief underlying these areas can be sensed.
 17. The method as claimed in claim 2, wherein the dangerous sub-zones of step b) are identified according to a second hypothetical path of the aircraft such that: if the aircraft is ascending, the ascent is stopped immediately, in other cases, the path is continued unchanged.
 18. The method as claimed in claim 2, wherein the time ΔT of step c) is computed according to a hypothetical flight time toward a dangerous sub-zone, calculated according to a time T_(pull) to place the aircraft in a horizontal path and a time T_(roll) to place the aircraft in a roll: in a horizontal plane when the aircraft is ascending or flying level, in a horizontal plane and in a vertical plane when the aircraft is descending.
 19. The method as claimed in claim 3, wherein the time ΔT of step c) is computed according to a hypothetical flight time toward a dangerous sub-zone, calculated according to a time T_(pull) to place the aircraft in a horizontal path and a time T_(roll) to place the aircraft in a roll: in a horizontal plane when the aircraft is ascending or flying level, in a horizontal plane and in a vertical plane when the aircraft is descending.
 20. The method as claimed in claim 7, wherein the time ΔT of step c) is computed according to a hypothetical flight time toward a dangerous sub-zone, calculated according to a time T_(pull) to place the aircraft in a horizontal path and a time T_(roll) to place the aircraft in a roll: in a horizontal plane when the aircraft is ascending or flying level, in a horizontal plane and in a vertical plane when the aircraft is descending. 